The present invention relates to a method and an arrangement for treating silicon plates, so-called wafers, for the manufacture of integrated circuits.
1. Field of the Invention
More specifically, the present invention relates to a method of heating so-called wafers, and more particularly so-called single wafers, when manufacturing integrated circuits with the aid of CVD-techniques (Chemical Vapor Deposition), and of so-called back-etching wafers in accordance with a preferred embodiment.
The present invention thus relates to a method of depositing substances by pyrolytic decomposition or heterogenic gas-phase reaction, for instance the deposition of metals, metal silicides or dielectric materials.
2. Description of the Related Art
One type of CVD-reactor is a so-called cold-wall reactor, i.e., the reactor walls are cooled while the substrate is heated. While the substrate is being heated, gases of mutually different compositions and in mutually different mixtures are introduced into the reactor, so as to produce a desired atmosphere with which the desired deposition of one or more substances on the substrate can be achieved.
The known methods of heating the substrate involve heating said substrate by means of infrared radiation from a radiation source in the cold-wall reactor, or heating the wafer to a desired temperature by means of an electrical resistance heating device placed there beneath.
One serious problem with both of these methods is that other parts of the reactor, such as the substrate holder, the thermal radiation window and the process-gas conduits, are heated to such temperatures as to cause the substance or substances to deposit on these components. This deposition of substances on surfaces other than wafer surfaces means that control over the process will be lost after a number of runs have been made, because the deposition rate, the formation of particles and the gas composition will change. Consequently, it is necessary to clean the reactor after only some few runs. The reactor is normally cleansed with a fluorine-containing plasma generated with the aid of a so-called RF-electrode, which is normally operated at a frequency of 13.5 MHz.
It will be noted that as a result of this problem, the reactor will not function in the manner intended after a given number of runs and the result achieved in the furnace will become progressively poorer the more runs that are made after the last furnace cleaning operation.
Another problem related to the use of the aforesaid heating methods in such cold-wall reactors, is that the reactors do not include means for etching the substrate in situ in the reactor. In order to etch the substrate, either to clean the same or to remove deposited and scattered nucleation centers of, e.g., tungsten from silicon dioxide or silicon nitride when depositing thick layers of, e.g., tungsten to fill-in contact holes, it is necessary to move the substrate to another reactor, unless an additional RF-electrode is fitted in the reactor, with presumptive dirtying of the substrate as a result of said transfer. The presence of an additional RF-electrode also constitutes the presence of an additional contaminating source. By depositing and subsequent cleaning, depositing and cleaning, etc., it is possible to maintain selectivity, even in the case of tungsten thicknesses above 10 000 .ANG..
It can be mentioned by way of example that the aforementioned is particularly significant when applying the CVD-technique with regard to refractory metals and their silicides. The decreasing dimensions and the use of multi-layer metalization makes it necessary, e.g., to find replacement materials for polysilicon as control electrode material and conductor material, and to develop methods of overcoming the problem of covering in stages in multi-layer processes. One possible solution to these problems is the use of tungsten silicide as the control electrode and tungsten as the filling material in contact holes.
It can thus be seen that the ability to move between deposition phases and cleansing phases quickly and simply is becoming progressively more significant. Known cold-wall reactors are unsuitable in this respect, because the different substances used also form deposits on surfaces other than the substrate.